The invention relates to fluid flow machines in general, and more particularly to improvements in means for transmitting torque from the driving element (such as a motor-driven shaft) to one or more impellers of a centrifugal pump or another fluid flow machine. Still more particularly, the invention relates to improvements in means for transmitting torque to brittle impellers.
German Offenlegungsschrift No. 29 15 292 discloses a ceramic rotor which is secured to a metallic shaft by means of two star-shaped discs each of which has a hub and a set of radially outwardly extending prongs or arms. The discs flank the rotor which is provided with slightly conical surfaces abutting the respective sets of prongs. These prongs are elastic and engage the respective surfaces of the rotor in stressed condition. At least one of the discs is form-lockingly connected with the rotor.
The purpose of the just described mounting of the rotor is to ensure that the rotor will be acted upon by compressive stresses but will be subjected to the action of negligible forces which could cause the development of tensional stresses, i.e., of stresses which cannot be readily withstood by a brittle material (such as a ceramic or glass). A drawback of the discs which are proposed in the Offenlegungsschrift is that their initial cost is substantial. Moreover, such discs can properly engage only a rotor which is of special design so that it can cause at least some stressing of the prongs and can be maintained in requisite form-locking engagement with one or both discs. Still further, at least one of the discs interferes with the flow of conveyed material toward, in and from the rotor if the latter constitutes an impeller. This holds true especially for the suction side of an impeller because the suction side is normally adjacent several indispensable or optional component parts of the pump, such as devices for engaging the periphery of the impeller.